Dead (devitalised) teeth are teeth whose nerve has been removed because of inflammation and that have had root canal treatment. They are easy to recognise on an X-ray, because their canals are filled with a material that shows up on X-rays. In the mouth, these teeth sometimes look slightly darker than the others.
In some cases there may be residual ‘hidden’ inflammation in the root that causes no symptoms, but when the tooth is moved with braces or aligners it can flare up, and the root canal treatment may need to be redone.
Moving dead teeth orthodontically is no different from moving any other teeth – they move at the same speed and are not at risk, as long as the roots are healthy and there is no inflammation.
This answer is for general information. Your own case needs an examination by an orthodontist.